Electro-optical modulator having high extinction ratio when functioning as switch

Abstract

An electro-optic modulator includes a substrate, an end-to-end Y-shaped waveguide for optical divergence and convergence, and electrodes. The waveguide is formed in the substrate and the electrodes are formed to substantially sandwich the waveguide in the substrate and voltages applied to the electrodes act to modulate first and second sections of the waveguide such that the optical outputs by the first and second sections are equal or opposite to each other in all necessary respects regarding phase and amplitude, and an improved extinction ratio thus obtained.

What is claimed is: 
     
         1 . An electro-optic modulator, comprising:
 a substrate;   a Y-shaped waveguide formed in the substrate and comprising a first Y-shaped section and a second Y-shaped section, the first Y-shaped section comprising a first branch and a second branch, the second Y-shaped section comprising a third branch and a fourth branch, the second and fourth branches being positioned at two opposite sides of the first and third branches; the substrate defining first to third recesses, the first and third recesses being located at two opposite sides of the waveguide, the second recess being located between the first and second sections;   a first ground electrode fully filling the first recess;   a first modulating electrode positioned on the substrate and located between the first and second branches;   a second ground electrode fully filling the second recess;   a second modulating electrode positioned on the substrate and covering the third branch;   a third ground electrode positioned on the substrate and covering the fourth branch; and   a third modulating electrode fully filling the third recess.   
     
     
         2 . The modulator of  claim 1 , wherein the substrate is made of lithium niobate crystal. 
     
     
         3 . The modulator of  claim 1 , wherein the waveguide is made of lithium niobate crystal diffused with titanium. 
     
     
         4 . The modulator of  claim 1 , wherein the waveguide comprises an input section and an output section, and the first and second sections diverge from the input section and are converged into the output section. 
     
     
         5 . The modulator of  claim 1 , wherein the first section comprises a first input branch and a first output branch, and the first and second branches diverge from the first input branch and are converged into the first output branch. 
     
     
         6 . The modulator of  claim 1 , wherein the second section comprises a second input branch and a second output branch, and the third and fourth branches diverge from the second input branch and are converged into the second output branch. 
     
     
         7 . The modulator of  claim 1 , wherein the first to fourth branches are parallel with each other. 
     
     
         8 . The modulator of  claim 7 , wherein the first to third recesses are rectangular and parallel with the first to fourth branches. 
     
     
         9 . The modulator of  claim 8 , wherein the firs recess has the same length as and is aligned with the second branch. 
     
     
         10 . The modulator of  claim 8 , wherein the third recess has the same length as and is aligned with the fourth branch. 
     
     
         11 . The modulator of  claim 8 , wherein orthogonal projections of the first and third recesses on the second recess fall within the second recess. 
     
     
         12 . The modulator of  claim 7 , wherein the first modulating electrode, the second modulating electrode, and the third ground electrode are strip-shaped and parallel with the first to fourth branches. 
     
     
         13 . The modulator of  claim 1 , wherein the first modulating electrode has the same length as and is aligned with the second branch. 
     
     
         14 . The modulator of  claim 1 , wherein the second modulating electrode and the third ground electrode have the same length as and are aligned with the fourth branch. 
     
     
         15 . The modulator of  claim 1 , comprising a buffer layer formed and sandwiched between the substrate and the second modulating electrode and between the substrate and the third modulating electrode. 
     
     
         16 . The modulator of  claim 15 , wherein the buffer layer is made of silicon dioxide.